Fast switching liquid crystal compositions for use in bistable liquid crystal devices

ABSTRACT

The invention is directed to the use of a fast switching liquid crystal composition said composition comprising at least 30 weight % of a component (α) containing one or more compounds having a dielectric anisotropy Δε of at least 25, whereby at least 25 weight % of said compounds have a dielectric anisotropy Δε of at least 40; and at least 5 weight % of a component (δ) containing one or more compounds having a ratio of γ 1 /T NI   K  of 0.51 mPa·s/K or less, a clearing point T NI  of at least 100° C. and a rotational viscosity γ 1  of not more than 190 mPa·s (wherein γ 1  is the rotational viscosity at 20° C. in mPa·s and T NI   K  is the clearing point in degrees Kelvin); in a bistable liquid crystal device and especially in a zenithal bistable nematic liquid crystal device, a nematic liquid crystal medium, and a bistable liquid crystal device comprising said fast switching liquid crystal composition.

The invention is directed to the use of a fast switching liquid crystalcomposition in a bistable liquid crystal device and especially in azenithal bistable nematic liquid crystal device, a nematic liquidcrystal medium, and a bistable liquid crystal device comprising the fastswitching liquid crystal composition.

Electrooptical devices utilizing liquid crystal media for displayinginformation are well known and used in a wide variety of technicalapplications (see, for a review, H. Kawamoto, Proc. IEEE, 90, 460(2002)). Among these, nematic liquid crystal devices are the mostprominent; there are, for instance, twisted nematic (TN) liquid crystaldevices (M. Schadt and W. Helfrich, Appl. Phys. Lett., 18, 127 (1971))and super-twisted nematic (STN) liquid crystal devices (see, inter alia,T. J. Scheffer and J. Nehring, Appl. Phys. Lett., 48,1021 (1984)). Thesedevices are monostable, i.e. the liquid crystal medium is switched to anON state by application of a suitable voltage, and is allowed to switchto an OFF state when the voltage applied falls below a lower voltagelevel. In order to display complex information electrooptical devicesneed to comprise a number of picture elements that can be switchedindependently of each other. However, when direct or even multiplexaddressing of pixels are used, the number of elements addressable innematic liquid crystal displays is limited, in the first case by meregeometrical requirements of the electrical connections and in the secondcase by the steepness of the device's transmission versus the voltagecurve.

This limitation can be overcome by incorporating thin film transistors(TFT) into each picture element. Such devices, also known as activematrix (AM) displays, enable addressing of a high number of pictureelements and thus of large area high resolution displays and withrelatively low voltage requirements. Some of these devices are alsomechanically rather stable and have a wide temperature range. Althoughthis allows the construction of small and portable battery powereddisplays, for certain applications the techniques has several drawbacks.Manufacturing AM displays is still a complicated process involving thebuilding up of a complex assembly which contributes to rather high costsof production. Since the device has no intrinsic or internal memory,constant update of the display even for static images is required. Thiscauses relatively high power consumption and, hence, rather poor batterylife time. This is especially undesired with portable devices displayinginformation that is changed only from time to time or in a limited partof the display such as mobile phones, personal digital assistants(PDAs), pagers, electronic shelf edge labels, and the like.

An approach to avoid the limitations and drawbacks of these nematicliquid crystal devices is to use displays with an internal memoryeffect, e.g. a bistable liquid crystal device. Bistability means thatthe molecules of the liquid crystal medium inside the device can adopttwo (or more) different stable states. Consequently, by applying asuitable addressing scheme the liquid crystal molecules of the mediumare switched into a first stable state which persists even afteraddressing; utilization of another addressing scheme causes the liquidcrystal molecules to adopt a second stable state that likewise persistsafter addressing.

Ferroelectric liquid crystal displays using smectic liquid crystalmaterials can be made into bistable devices. They have, however, severaldisadvantages, e.g. lack of shock resistance, narrow operatingtemperature range, and low cell gap causing manufacturing difficulties.Therefore, these ferroelectric devices are unlikely to fulfill therequirements to displays for the portable devices mentioned above.

However, not only ferroelectric smectic liquid crystals are capable ofbeing used in bistable devices but also nematic liquid crystals. Besidesother approaches that utilize bistable bulk configurations adopted bynematic liquid crystals (see, for instance, I. Dozov et al., “Recentimprovements of bistable nematic displays switched by anchoring breaking(BiNem®)”, Proceedings SID 01 (2001), 16.1, 224 and referencestherewithin), a promising way of achieving bistability in a nematicliquid crystal display is to use a surface alignment which can supporttwo or more stable states. As discussed in literature (see, forinstance, J. C. Jones, G. Bryan-Brown, E. Wood, A. Graham, P. Brett andJ. Hughes, “Novel bistable liquid crystal displays based on gratingalignment”, in “Liquid Crystal Materials, Devices, and Flat PanelDisplays”, R. Shashidhar, B. Gnade, Eds., Proceedings of SPIE Vol. 3955(2000), 84 and references cited therein) two types, azimuthal andzenithal bistability, can be distinguished.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Illustration of zenithal bistability using grating alignment(with the lines indicating the local director) showing a) the high tilt(continuous) and b) the low tilt (defect) states.

FIG. 2. The a) VAN and b) TN geometries for ZBD showing the directordistribution of the high and low tilt states.

FIG. 3. The τ-V curve for MLC-6204-000 at 25° C. (pulse duration or timeslot vs. voltage). The switching voltage (V_(100 μs)) and operatingwindow (ΔV_(400 μs)) used for comparisons are indicated.

In the first instance (i.e. azimuthal bistability), the director of theliquid crystal molecules in the display having a grating alignment onthe surface of one of the display cell's plates (or substrates) will lieparallel to said plate in both stable states; that means that switchingbetween the stable states occurs within the plane of the display cell'splates (see, for instance, WO 92/00546 and WO 95/22077 which describesthe use of a substrate having a bigrating alignment layer). However,reproducing selection of the stable states is found to be difficult andswitching generally requires a high switching voltage.

On the other hand, zenithal bistability is observed when the zenithalbistable surface is used (see FIG. 1; the tiny lines represent the localdirector of the liquid crystal molecules that are oriented byinteraction with the surface grating and appropriate alignment layer).With such a surface, the director of the liquid crystal molecules hastwo possible configurations with different pretilt angles in the sameazimuthal plane (i.e. the plane perpendicular to the surface of thedisplay cell's substrate). The first state is the high tilt state whilethe second state is the low tilt state. The grating of the zenithalbistable surface is defined by its amplitude a and its pitch L; typicalvalues are for L of about 1 μm and for a of about 0.6 to 0.8 μm (see WO97/14990 and, for more details, WO 02/08825; and J. C. Jones, G.Bryan-Brown, E. Wood, A. Graham, P. Brett and J. Hughes, “Novel bistableliquid crystal displays based on grating alignment”, in “Liquid CrystalMaterials, Devices, and Flat Panel Displays”, R. Shashidhar, B. Gnade,eds., Proceedings of SPIE Vol. 3955 (2000), 84).

A homeotropic orientation can be, for example, induced by coating thegrating with a homeotropic alignment layer, this orientation ensuresthat the director of the liquid crystal molecules does not lie parallelto the grooves of the grating. Although the orientation of the directorof the liquid crystal molecules is perpendicular to the (local) surface,i.e. varying with the location on the surface along a directionperpendicular to the grooves, the orientation in the “bulk” is very muchinfluenced by the opposite surface alignment in both states. Switchingfrom one stable state to the other may be achieved by applying a simpleelectrical pulse thereby causing a switch from a black display orpicture element to a white one (or vice versa) with the appropriatepolariser configuration and retardation, and switching back to theoriginal state occurs upon application of a pulse of opposite polaritythereby causing a switch from white to black (or vice versa). Switchingmay also be induced by using pulses of same polarity but with muchhigher voltages (also referred to as “reverse switching”); however,reverse switching is a detrimental effect which limits the operation ofa zenithal bistable nematic device in terms of the addressing and so ahigh a voltage as possible is desired for the reverse switching.

In general, for obtaining zenithal bistability only one of the twodisplay cell's substrates is provided with a surface grating. Theopposite plate may have a surface providing a homeotropic alignment ofthe liquid crystal director (VAN mode, see FIG. 2 a)) or a surfaceinducing planar alignment of the director (twisted mode, see FIG. 2 b))thereby causing the twisting of the liquid crystal director around theaxis perpendicular to the substrates across the cell for the low tiltstate. For details with regard to cell geometry and configuration, exactcell parameters, addressing means, assembling of the entire zenithalbistable device (including use of polarisers) and so on, see thedisclosure of WO 97/14990, E. L. Wood, G. P. Bryan-Brown, P. Brett, A.Graham, J. C. Jones, and J. R. Hughes, “Zenithal Bistable Device (ZBD™)Suitable for Portable Applications, SID 00 Digest (2000), 124, J. C.Jones, J. R. Hughes, A. Graham, P. Brett, G. P. Bryan-Brown, and E. L.Wood, “Zenithal Bistable Devices: Towards the electronic book with asimple LCD”, IDW '00 (2000), 301, J. C. Jones, S. M. Beldon and E. L.Wood, “Greyscale in Zenithal Bistable LCD: The Route to Ultra-low PowerColour Displays”, seminar talk on the ASID meeting 2002 of the Societyfor Information Display, Singapore, September 2002; and the detaileddiscussion given in J. C. Jones, G. Bryan-Brown, E. Wood, A. Graham, P.Brett and J. Hughes, “Novel bistable liquid crystal displays based ongrating alignment”, in “Liquid Crystal Materials, Devices, and FlatPanel Displays”, R. Shashidhar, B. Gnade, eds., Proceedings of SPIE Vol.3955 (2000), 84, and references cited therein.

Utilizing zenithal bistability in electrooptical devices offersattractive features:

-   -   Image retention on a display without continuous update combined        with    -   High mechanical shock stability    -   Low power consumption since the display only needs addressing        when the image changes    -   Infinite multiplexibility for unlimited resolution without the        need for TFT elements    -   Transmissive and reflective modes possible    -   Suitability for use with plastic substrates

Besides the assembly and make up of the zenithal bistable display,another key issue to the zenithal bistable device technology is thenematic liquid crystal medium used inside the display's cell.

The zenithal bistable device and hence the liquid crystal medium have tomeet several requirements more or less depending on the specific use ofthe device. Since there is no consistent theory so far that mightpredict the physical variables to be optimized, it turned out to behelpful using a set of (semi-)empirical parameters for evaluating liquidcrystal media with respect to their usefulness in zenithal bistablenematic devices. These are illustrated in the so-called τ-V curve forswitching voltages of pulse duration τ and for 10 and 90% switchinglevels with opposite polarities (see FIG. 3) for a liquid crystalmixture of the prior art, namely MLC-6204-000 of Merck KGaA, Darmstadt,Germany.

Firstly, in order to minimize power consumption, to allow moreflexibility with the addressing of the device's picture elements and toremain within the limits of standard STN drivers a low switching fieldand correspondingly a low operating voltage is desirable for switchingfrom one bistable state to the other. For material comparison one candetermine the switching field E for a pulse (usually a 100 μs pulseduration) from the switching voltage V that gives a transmission changefrom, e.g., 0 to 90% transmission (black-to-white; B-W) for a particularliquid crystal mixture in a given test cell providing zenithalbistability. (In general, one can also use the 100 to 10% transmissionchange transition of white-to-black, W-B, where the switching field ofwhich may be higher or lower than the B-W transition depending on thegrating's shape and dimensions.) In order to take into account thevoltage drop across the grating (which varies for different types ofgratings as well as cell thickness) the value of E actually measured iscorrected to distinguish the field just across the liquid crystal againfor comparison purposes giving the corrected switching fieldE_(LC@100 μs) for a 100 μs pulse. Here, an additional factor of 1.5 μmis added to the cell thickness d when calculating the field just acrossthe liquid crystal:E _(100 μs) =V _(100 μs) /d and E _(LC@100 μs) =V _(100 μs)/(d+1.5)where d is in μm.

Multiplying E_(LC@100 μs) with optimum cell gap d_(opt) (that can beapproximated by using the TN 1^(st) minimum condition d_(opt)=λ√3/(2Δn)with λ=555 nm and Δn being the optical anisotropy of the liquid crystalmedium) gives the operating voltage V_(opt) corresponding to the optimumcell gap for a 100 μs pulse for just the liquid crystal. E_(LC@100 μs)and so V_(opt) depend on the liquid crystal medium used. (The optimumcell gap is considered only for the twisted mode (see FIG. 2 b)) herebut comparisons can also be made for the VAN mode (see FIG. 2 a)), wherethe retardation of the hybrid state will be matched to either ahalf-wave plate of quarter-wave plate depending on the polariserconfiguration (dΔn=λ/2 and dΔn=λ/4, respectively).

The second empirical parameter that needs to be taken into account isthe operating window ΔV_(opt) corresponding to the optimum cell gap. Itdescribes the effect of reverse switching: When applying a pulse with agiven time slot of, e.g. 400 μs, and a defined pulse polarity, e.g. B-W,one observes the desired switching at a specific value of the switchingfield and a further reverse switching (e.g. W-B in this case) which isnot induced by a pulse of inverse polarity but by a pulse of the samepolarity at an increased switching field. For technical purposes,obviously said operating window ought to be as wide as possible topermit more flexibility of the driving schemes used and particularly inrelation to achieving good grayscale operation (see J. C. Jones, S. M.Beldon and E. L. Wood, “Greyscale in Zenithal Bistable LCD: The Route toUltra-low Power Colour Displays”, seminar talk on the ASID meeting 2002of the Society for Information Display.) It can be represented byΔE_(LC@400 μs), that is the corrected difference between the 90% reverseswitching field and the 90% B-W switching field for a 400 μs pulse:ΔE _(400 μs) =ΔV _(400 μs) /d and ΔE _(LC@400 μs) =ΔV _(400 μs)/(d+1.5)where d is in μm.

Taking into account the optimum cell gap d_(opt) by multiplying withΔE_(LC@400 μs) eventually gives the operating window ΔV_(opt)(d_(opt)ΔE_(LC@400 μs)=ΔV_(opt)).

Still another parameter of great importance is the clearing point T_(NI)of the liquid crystal medium describing the temperature at which thenematic mixture becomes isotropic. For many technical purposes and forincreasing the variability of electrooptical devices utilizing zenithalbistability (and so the possible applications), liquid crystal mediahaving a high clearing point, preferably of at least 80° C. or more, aredesired.

A further parameter, the optical response time τ_(opt) corresponding tothe optimum cell gap, describes how fast the liquid crystal mediumchanges between stable states upon application of an electric pulse. Itcan be determined by measuring the response time τ for the 10-90% B-Wtransition using a 100 μs pulse in the actual test cell; then, in orderto normalize the experimental values, τ is multiplied by (d_(opt)/d)²giving τ_(opt) (with d_(opt) being the optimum cell gap as calculatedabove for V_(opt) and d being the actual cell gap of the test cellused). The W-B transition is much faster (less than 1 ms) and so indeedthe B-W response time is of most importance when assessing theproperties of the liquid crystal medium used. The smaller τ_(opt) thefaster the optical response of the liquid crystal medium. A smallτ_(opt) (of about 40 ms or, preferably, less than about 30 ms) may bedesirable for certain electrooptical applications, e.g. displayingmoving pictures. It is even more preferred for specific videoapplications that τ_(opt) is less than about 16 ms so as not to observeflash.

Those liquid crystal media the use of which in zenithal bistable deviceshave been described in the prior art do not meet all the parameterrequirements outlined above. Even liquid crystal mixture MLC-6204-000(available from Merck KGaA, Darmstadt, Germany) that has been used inzenithal bistable devices as the preferred medium (WO 01/40853, Example6; J. C. Jones, G. Bryan-Brown, E. Wood, A. Graham, P. Brett and J.Hughes, “Novel bistable liquid crystal displays based on gratingalignment”, in “Liquid Crystal Materials, Devices, and Flat PanelDisplays”, R. Shashidhar, B. Gnade, Eds., Proceedings of SPIE Vol. 3955(2000), 84) has a clearing point T_(NI) of only 62.4° C. that is ratherlow for use in zenithal nematic bistable device for many possibleapplications. Furthermore, its τ_(opt) is above 40 ms that is ratherhigh for use in zenithal nematic bistable device for some specificapplications requiring a small optical response time τ_(opt).

The present invention therefore encounters the problem to provide aliquid crystal composition that is suitable for use in a bistable liquidcrystal device and especially in a zenithal bistable nematic device andhas an improved set of properties.

The problem is solved by the use of a liquid crystal composition in abistable liquid crystal device, said device being preferably a zenithalnematic liquid crystal device, whereby said compostion comprises

-   -   at least 30 weight % (based on the total weight of the        composition) of a component (α) containing one or more compounds        having a dielectric anisotropy Δε of at least 25, whereby at        least 25 weight % (based on the total weight of the composition)        of said compounds have a dielectric anisotropy Δε of at least        40; and    -   a component (δ) containing one or more compounds each having a        ratio of γ₁/T_(NI) ^(K) of 0.51 mPa·s/K or less, a clearing        point T_(NI) of at least 100° C. and a rotational viscosity γ₁        of not more than 190 mPa·s (wherein γ₁ is the rotational        viscosity at 20° C. in mPa·s and T_(NI) ^(K) is the clearing        point in degrees Kelvin).

(The dielectric anisotropy, the rotational viscosity and the clearingpoint can be determined according to the methods described in “PhysicalProperties of Liquid Crystals—Description of the measurement methods”,ed. W. Becker, Merck KGaA, Darmstadt, 1998, whereby values for singlecompounds may be extrapolated from those determined using a knownconcentration (usually 10 weight % of the single compound) in a standardhost mixture (usually ZLI-4792 of Merck KGaA, Darmstadt, Germany) forwhich the initial mixture values are also known. Further parameters ofsingle compounds may be obtained similarity.)

A further subject matter of this invention is a bistable liquid crystaldevice comprising

-   -   two outer substrates which, together with a frame, form a cell;        -   a liquid crystal composition present in said cell;        -   electrode structures with alignment layers on the inside of            said outer substrates whereby at least one alignment layer            comprises an alignment grating that permits the liquid            crystal composition to adopt at least two different stable            states whereby the assembly of said electrode structures            with said alignment layers being such that a switching            between the said at least two different stable states is            achieved by applying suitable electric signals to said            electrode structures;        -   whereby said liquid crystal composition is said liquid            crystal composition as described above and below and that            comprises said components (α) and (δ).

In particular, said bistable liquid crystal device is a zenithalbistable nematic liquid crystal device in which said electrodestructures with alignment layers on the inside of said outer substrateshave at least one alignment layer that comprises an alignment gratingthat permits the compounds of said liquid crystal composition to adoptat least two different stable states with different pretilt angles inthe same azimuthal plane whereby the assembly of said electrodestructures with said alignment layers being such that a switchingbetween the said at least two different stable states is achieved byapplying suitable electric signals to said electrode structures.

It will be acknowledged that the invention is described hereinafterprimarily with regard to the use of the liquid crystal composition abovein a zenithal bistable nematic liquid crystal device although it may beused in other liquid crystal devices as well, for instance, in bistableliquid crystal devices like azimuthal bistable liquid crystal devices asdisclosed, inter alia, in WO 92/00546 and WO 95/22077. Thus, details aregiven for the zenithal bistable nematic liquid crystal device but caneasily be adapted to the requirements of other types of bistable liquidcrystal devices.

The zenithal bistable nematic device and the liquid crystal compositionfor use in a zenithal bistable nematic device according to the inventionshow an improved set of parameters said parameters being, inter alia,operating voltage, operating window, and, especially, clearing point. Itshould be noticed that, for instance, the clearing point of the liquidcrystal compositions for use in the zenithal bistable nematic devices ofthe invention is significantly higher than the clearing point of liquidcrystal mixtures previously used in zenithal bistable nematic devices.Operating voltage and operating window are both in a range useful foroperating of a zenithal bistable nematic device. Furthermore, in thepreferred embodiments of the invention the optical response time τ_(opt)is decreased significantly so that fast switching liquid crystalcompositions for use in bistable liquid crystal devices and especiallyin zenithal bistable nematic liquid crystal devices are obtained.

The cell that is part of the zenithal bistable nematic device accordingto the invention may be any conventional cell which allows the nematicliquid crystal composition to adopt at least two different zenithalbistable states. Two possible stable states are schematically depictedin FIG. 1. The two different zenithal bistable states are characterizedby two different pretilt angles that are adopted by the liquid crystalmolecules in the same azimuthal plane. The cell comprises a frame andtwo outer substrates or plates and has electrode structures withalignment layers on the inside of said substrates. At least one of thesealignment layers has an zenithal alignment grating known to thoseskilled in the art and as described, for instance, in WO 97/14990, WO01/40853, WO 02/08825, and J. C. Jones, et al., Proceedings of SPIE Vol.3955 (2000), 84.

The electrode structures are assembled with the alignment layer(s) insuch a way that (in the case of two stable states) switching from onestable state to the other can be achieved by applying suitable electricsignals to the electrode structures thereby applying said electricsignals to the liquid crystal composition inside the cell. Commonly,single pulses can be used as such suitable electric signals. Details areknown to the artisan and described in WO 97/14990, WO 01/40853, WO02/08825, J. C. Jones, J. R. Hughes, A. Graham, P. Brett, G. P.Bryan-Brown, IDW '00 (2000), 301, J. C. Jones, et al., Proceedings ofSPIE Vol. 3955 (2000), 84, and E. L. Wood, P. J. Brett, G. P.Bryan-Brown, A. Graham, R. M. Amos, S. Beldon, E. Cubero and J. C.Jones, “Large Area, High Resolution Portable ZBD Display”, SID 02 Digest(2002), 22-25.

The substrate opposite to the substrate having the grating alignmentlayer may have an homeotropic alignment due to suitable surfacetreatment (see FIG. 2 a)). Switching upon application of an electricpulse occurs from the high tilt or vertically aligned state to the lowtilt or hybrid aligned state. This switch gives a black-to-white (B-W)change if the cell is placed between crossed polarizers (at 45° to thegrating direction), with the brightest white state obtained when thevertically aligned state acts as a half-waveplate (dΔn=λ/2). Thisswitching mode is called VAN mode. Zenithal bistable devices utilizingthe VAN mode are very insensitive to cell gap variations. They requireadditional optical compensators to achieve wide viewing angles. A secondswitching mode of zenithal bistable devices is called TN mode (see FIG.2 b)): The substrate opposite to the substrate having the gratingalignment layer has a alignment layer, usually of rubbed polyimide,causing planar alignment of the liquid crystal molecules on saidsubstrate. This in turn causes the twisting of the liquid crystaldirector around their axis perpendicular to the substrates across thecell. Switching upon application of an electric pulse now occurs fromthe low tilt or twisted aligned state to the high tilt or hybrid alignedstate. This switch gives a black-to-white (B-W) change if the cell isplaced between parallel polarizers and using the slightly modified TN1^(st) minimum condition (as given above) accounting for the influenceof the ordinary refractive index of the hybrid state. Due to a highnormal incidence contrast ratio additional optical compensators forachieving wide viewing angles are not required in a transmissivedisplay. Therefore the TN mode is preferred for most of the technicalapplications of zenithal bistable nematic devices. It is also possibleto build up a zenithal bistable reflective display and even a zenithalbistable transflective display. For details, also with regard to thepolarizers used, it is referred to WO 97/14990, E. L. Wood, G. P.Bryan-Brown, P. Brett, A. Graham, J. C. Jones, and J. R. Hughes, SID 00(2000), 124, and E. L. Wood, P. J. Brett, G. P. Bryan-Brown, A. Graham,R. M. Amos, S. Beldon, E. Cubero and J. C. Jones, “Large Area, HighResolution Portable ZBD Display” SID 02 Digest (2002), 22-25.

In the context of the present invention and with respect to thecompounds contained in the liquid crystal composition for use inbistable liquid crystal devices and especially in zenithal bistablenematic devices of the invention the term “alkyl” means—as long as it isnot defined in a different manner elsewhere in this description or theclaims—straight-chain and branched hydrocarbon (aliphatic) radicals with1 to 15 carbon atoms; the hydrocarbon radicals may be unsubstituted orsubstituted with one or more substituents being independently selectedfrom the group consisting of F, Cl, Br, I or CN. This subclass of“alkyl” containing aliphatic saturated radicals may also be designatedas “alkanyl”. Furthermore, “alkyl” is also meant to compriseunsubstituted or likewise substituted hydrocarbon radicals in which oneor more of the CH₂ groups are such replaced by —O— (“alkoxy”,“oxaalkyl”), —S— (“thioalkyl”), —CH═CH— (“alkenyl”), —C≡C— (“alkinyl”),—CO—O— or —O—CO— that there are no adjacent hetero atoms (O, S).Preferably, alkyl is a straight-chain or branched saturated hydrocarbonhaving 1, 2, 3, 4, 5, 6, 7 or 8 carbon atoms and being unsubstituted ormono- or poly-substituted with F. More preferably, alkyl is meant to bemethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl,neopentyl, n-hexyl, n-heptyl, n-octyl; CF₃, CHF₂, CH₂F; CF₂CF₃. Mostpreferably, alkyl is a straight-chain hydrocarbon of up to 8 carbonatoms.

Since one or more CH₂ groups of an alkyl radical may be replaced by —O—as described above, the term “alkyl” also comprises “alkoxy” and“oxaalkyl” moieties. “Alkoxy” means “O-alkyl” in which the oxygen atomis directly linked to the group or ring being substituted with alkoxyand alkyl is defined as above. In particular, “alkyl” in “O-alkyl” meansmethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl,neopentyl, n-hexyl, n-heptyl or n-octyl, whereby alkyl is optionallysubstituted with F. Most preferably, alkoxy is —OCH₃, —OC₂H₅, —O-n-C₃H₇,—O-n-C₄H₉, —O-t-C₄H₉, —OCF₃, —OCHF₂, —OCHF or —OCHFCHF₂. In the contextof the present invention the term “oxaalkyl” comprises alkyl moieties inwhich at least one non-terminal CH₂ group is replaced by O in such a waythat there are no adjacent oxygen atoms. Preferably, oxaalkyl comprisesstraight-chain radicals of the formula C_(t)H_(2t+1)—O—(CH₂)_(u)— inwhich t and u are independently of each other 1, 2, 3, 4, 5 or 6;especially t is 1 or 2 and u is an integer from 1 to 6.

If one or more of the CH₂ groups of alkyl are replaced by sulfur a“thioalkyl” radical is obtained. Thioalkyl comprises alkyl moieties inwhich at least one terminal or non-terminal CH₂ group is replaced by S(sulfur) in such a way that there are no adjacent sulfur atoms.Preferably, thioalkyl comprises straight-chain radicals of the formulaC_(t)H_(2t+1)—S—(CH₂)_(u)— in which t is 1, 2, 3, 4, 5 or 6 and u is 0,1, 2, 3, 4, 5 or 6; especially t is 1 or 2 and u is zero or an integerfrom 1 to 6.

In the context of the present invention the term “alkenyl” means analkyl radical in which one or more —CH═CH— moieties are present. Whentwo —CH═CH— moieties are present the radical may also be designated as“alkadienyl”. An alkenyl radical may comprise 2 to 15 carbon atoms andmay be straight-chain or branched. It can be unsubstituted or mono- orpolysubstituted with F, Cl, Br, I or CN; one or more of its CH₂ groupsmay be replaced independently of each other by —O—, —S—, —C≡C—, —CO—O—,—OC—O— such that there are no hetero atoms adjacent to each other. Ifthe alkenyl CH═CH moiety is not a terminal CH₂═CH group it may exist intwo configurations, namely the E-isomer and the Z-isomer. In general,the E-isomer (trans) is preferred. Preferably, alkenyl contains 2, 3, 4,5, 6 or 7 carbon atoms and means vinyl, 1E-propenyl, 1E-butenyl,1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 2-propenyl, 2E-butenyl,2E-pentenyl, 2E-hexenyl, 2E-heptenyl, 3-butenyl, 3E-pentenyl,3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl,4Z-heptenyl, 5-hexenyl and 6-heptenyl. More preferred alkenyl is vinyl,1E-propenyl, 3E-butenyl.

In the case one or more CH₂ alkyl groups are replaced by —C≡C— analkinyl radical is obtained. Also the replacement of one or more CH₂alkyl groups by —CO—O— or —O—CO— is possible. The following of theseradicals are preferred: acetyloxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl,2-propionyloxyethyl, 2-butyryloxyethyl, 2-acetyloxypropyl,3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxycarbonyl)-ethyl, 3-(methoxycarbonyl)-propyl,3-(ethoxy-carbonyl)-propyl oder 4-(methoxycarbonyl)-butyl.

The liquid crystal composition for use in the (zenithal) bistable(nematic) liquid crystal device of the invention contains at least twodifferent components, component (α) and component (δ).

It has been found by the inventors that the liquid crystal compositionfor use in a bistable liquid crystal device needs to comprise acomponent (δ) which may influence the optical response time τ_(opt) asdesired. This component (δ) contains one or more compounds each having aratio of γ₁/T_(NI) ^(K)≦0.51 mPa·s/K, a clearing point T_(NI)≧100° C.and a rotational viscosity γ₁≦190 (wherein γ₁ is the rotationalviscosity at 20° C. in mPa·s and T_(NI) ^(K) is the clearing point indegrees Kelvin).

It is preferred that component (δ) contains at least one compound havinga ratio of γ₁/T_(NI) ^(K) of 0.46 mPa·s/K or less, a clearing pointT_(NI) of at least 110° C. and a rotational viscosity γ₁ of not morethan 180 mPa·s. It is even more preferred that the ratio of γ₁/T_(NI)^(K) is 0.42 mPa·s/K or less, the clearing point T_(NI) is of at least120° C. and the rotational viscosity γ₁ of said compound is of not morethan 175 mPa·s.

Component (δ) may be present in an amount of about 5 weight % (based onthe total weight of the composition) but usually not more than about 65weight %. It is preferred that its amount is in the range from about 7to about 50 weight %, more preferred in the range from about 10 to about35 weight %.

It is further preferred that said component (δ) comprises at least onecompound of formula I

in which

-   R¹¹ and R¹² are independently of each other C₁-C₁₅ alkyl which is    unsubstituted or mono- or poly-substituted with CN or halogen and in    which one or more of the CH₂ groups may be replaced independently of    each other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that    there are no hetero atoms adjacent to each other;

in which

-   L¹¹ and L¹² are independently of each other H or F; and

in which

-   L¹³ and L¹⁴ are independently of each other H or F.

Preferred compounds of formula I are compounds of one of the formulasI-A to I-I

wherein m and r are independently of each other 2, 3, 4, 5, 6 or 7, nand q are independently of each other 1, 2, 3, 4, 5, 6 or 7, and p is 4,5, 6, 7 or 8.

More preferred are compounds of formulas I-A and I-B, i.e. compounds offormula I in which R¹¹ is alkenyl with up to 7 carbon atoms oralkadienyl with up to 8 carbon atoms, R¹² is alkanyl with up to 7 carbonatoms, the ring indicated by A is a cyclohexyl ring, and the ringindicated by B is a phenyl ring. Also, compounds of formulas I-D, I-E,I-G, I-H and I-I are likewise preferred. Especially preferred arecompounds of formula I-A with m being 2, 3, 4 or 5 and n being 1, 2, 3or 4.

Specific examples of compounds according to formula I are the following:

with I1 and I3 being the most preferred ones.

The following table, Table 1, shows the values of γ₁ (in mPa·s), T_(NI)(in degrees Celsius, ° C.) and γ₁/T_(NI) ^(K) (in mPa·s/K) for somespecific examples of compound I that is preferably comprised bycomponent (δ).

TABLE 1 Compound γ₁/mPa · s T_(NI)/ ° C. γ₁/T_(NI) ^(K)/mPa · s/K I1 118161 0.27 I3 159 181 0.35 I5 118 192 0.25 I6 100 175 0.22 I7 149 190 0.32I8 154 124 0.39 I9 174 138 0.42 I10 157 265 0.29 I11 94 220 0.19 I12 88116 0.23 I13 111 154 0.26

The other component required according to the invention, component (α),contains one or preferably more compounds having a high dielectricanisotropy Δε of 25 or more, especially of 30 or more. At least 25weight %, preferably 30 weight % or more, (based on the total weight ofthe composition) of the compounds of component (α) exhibit a dielectricanisotropy Δε of 40 or more. At least 30 weight % (based on the wholecomposition) of component (α) need to be comprised by the liquid crystalcomposition of the zenithal bistable nematic device according to theinvention. It is preferred that the liquid crystal composition comprises35 weight % or more, even more preferred at least 40 weight %, stillmore preferred at least 45 weight %, most preferred 50 weight % or more,of said component (α).

It is preferred that said component (α) comprises at least one compoundof formula II and/or at least one compound of formula III

in which

-   a, b, c and d are independently of each other 0, 1, 2, 3 or 4;-   R²¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- or    poly-substituted with CN or halogen and in which one or more of the    CH₂ groups may be replaced independently of each other by —O—, —S—,    —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms    adjacent to each other;-   R³¹ is C₂-C₁₅ alkenyl which is unsubstituted or mono- or    poly-substituted with CN or halogen and in which one or more of the    CH₂ groups may be replaced independently of each other by —O—, —S—,    —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms    adjacent to each other;-   Z²¹ and Z³¹ are independently of each other a single bond or —C≡C—.

It has been found by the inventors that component (α) preferablycomprises either one or more compounds of formula II or one or morecompounds of formula III or one or more compounds of both formula II andformula III (besides other compounds having the required high dielectricanisotropy that may be present). In one preferred embodiment of theinvention component (α) contains at least one compound of formula II butno compound of formula II; in another preferred embodiment component (α)contains at least one compound of formula III but no compound of formulaII. If component (α) contains at least one compound of formula II, saidcompound(s) of formula I may be present in a total amount of at least 5weight %, preferably at least 10 weight %, more preferred at least 15weight % or more. If component (α) contains one compound of formula III,said compound of formula II may be present in an amount of about 5 to 30weight %, preferably 8 to 25 weight %, more preferred 10 to 20 weight %.However, if component (α) contains more than one compound of formulaIII, the total amount of these compounds is in the range of about 5 toabout 55 weight %, preferably about 8 to about 35 weight %, morepreferred about 9 to about 25 weight %.

With regard to compounds of formula II a and b may be independently ofeach other 0, 1, 2, 3 or 4, preferably 0, 1 or 2; that means thatpreferably each of the phenyl rings of formula II may be unsubstitutedor mono- or di-substituted with fluorine. If present the Fsubstituent(s) may be in any position of the phenyl ring substituted. Itis preferred that and/or

are independently of one another

with L²¹ and L²² being independently of one another H or F. Furthermore,Z²¹ can be either a single bond (so that the CN group is directly linkedto the phenyl ring) or a C—C triple bond thereby forming a —C≡C—CNsubstituent of the phenyl ring. It is preferred that Z²¹ is a singlebond.

Preferred compounds of formula II are the following compounds:

with R²¹ being defined as above. Preferably, R²¹ in formulas II and II-Ato II-M is a straight-chain alkyl radical, especially an alkanyl radicalwith 1, 2, 3, 4, 5 or 6 carbon atoms. Highly preferred compounds are ofgeneral formula II-A1 with n=1, 2, 3, 4, 5 or 6.

Especially preferred examples of compounds of formula II being presentin component (α) either alone or in combination with each other are thefollowing compounds of formula II1 to II3:

It is preferred to have a mixture of all three compounds II1, II2 andII3 in the liquid crystal composition. For instance, compound II1exhibits a dielectric anisotropy Δε of 37.5 whereas compound II3 has aΔε of 36.0.

With regard to compounds of formula III c and d may be independently ofeach other 0, 1, 2, 3 or 4, preferably 0, 1 or 2; that means thatpreferably each of the phenyl rings of formula Ill may be unsubstitutedor mono- or di-substituted with fluorine. If present the Fsubstituent(s) may be in any position of the phenyl ring substituted. Itis preferred that and/or

are independently of one another

with L³¹ and L³² being independently of one another H or F. Furthermore,Z³¹ can be either a single bond (so that the CN group is directly linkedto the phenyl ring) or a C—C triple bond thereby forming a —C≡C—CNsubstituent of the phenyl ring. It is preferred that Z³¹ is a singlebond.

Preferred compounds of formula III are the following compounds:

with R³¹ being defined as above. Preferably, R³¹ in formulas III andIII-A to III-M is a straight-chain alkenyl radical, especially with 1,2, 3, 4, 5 or 6 carbon atoms and most preferred with a terminal C═Cdouble bond. Highly preferred compounds are of general formula III-B1with n =2, 3, 4, 5 or 6.

Especially preferred examples of compounds of formula III being presentin component (α) either alone or in combination with each other are thefollowing compounds of formula III1 to III4:

The most preferred compound of formula III is compound III4 whichexhibits a dielectric anisotropy Δε of 59.5.

It will be acknowledged that other compounds than those of formulas IIand III may be present in component (α) as long as they have asufficiently high dielectrical anisotropy Δε and are not detrimental tothe set of parameters as outlined above.

Thus, it is preferred that component (α) of the liquid crystalcomposition used in the zenithal bistable nematic device of theinvention also comprises one or especially more compounds of formula IV

in which

-   e and f are independently of each other 0, 1, 2, 3 or 4;-   R⁴¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- or    poly-substituted with CN or halogen and in which one or more of the    CH₂ groups may be replaced independently of each other by —O—, —S—,    —C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms adjacent    to each other (which means that R⁴¹ does not comprise any alkenyl    radical);-   Z⁴¹ is a single bond or —C≡C—.

With regard to compounds of formula IV e and f may be independently ofeach other 0, 1, 2, 3 or 4, preferably 0, 1 or 2; that means thatpreferably each of the phenyl rings of formula IV may be unsubstitutedor mono- or di-substituted with fluorine. If present the Fsubstituent(s) may be in any position of the phenyl ring substituted. Itis preferred that and/or

are independently of one another

with L⁴¹ and L⁴² being independently of one another H or F. Furthermore,Z⁴¹ can be either a single bond (so that the CN group is directly linkedto the phenyl ring) or a C—C triple bond thereby forming a —C≡C—CNsubstituent of the phenyl ring. It is preferred that Z⁴¹ is a singlebond.

Preferred compounds of formula IV are the following compounds:

with R⁴¹ being defined as above. Preferably, R⁴¹ in formulas IV and IVAto IV-M is straight-chain alkyl, especially straight-chain alkanylhaving 1, 2, 3, 4, 5, 6, 7 or 8 carbon atoms. Highly preferred compoundsare of general formulas IV-A1 and IV-B1 with n=1, 2, 3, 4, 5 or 6,whereby compounds of formula IV-A1 are most preferred.

Especially preferred compounds of formula IV are compounds of formulaIV1 to IV6:

Among these compounds of formulas IV1 (having a dielectric anisotropy Δεof 53.7), IV2, IV3 (Δε=44.9) and IV4 (Δε=43.0) are most preferred. Ifpresent the total amount of compounds of formula IV in the liquidcrystal composition for use in the zenithal bistable nematic devices ofthe invention may be about 10 weight % or more (although even smalleramounts are possible as well), preferably 20 weight % or more, morepreferred in the range of about 25 to 60 weight %, still more preferredin the range of about 35 to about 55 weight %. When used as a mixturedifferent compounds of formula IV may be contained in component (α) inan almost equal amount. For instance, if compounds of formulas IV1 toIV4 are used, they may be contained in an 1:1:1:1 ratio.

In another preferred embodiment of the invention component (α) of theliquid crystal composition for use in the zenithal bistable nematicdevices comprises at least one compound of formula XV:

in which

-   j is 0 or 1;-   R¹⁵¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- or    poly-substituted with CN or halogen and in which one or more of the    CH₂ groups may be replaced by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—,    —OC—O— such that there are no hetero atoms adjacent to each other;-   Z¹⁵¹ and Z¹⁵² are independently of each other a single bond or    —C≡C—;

-   -   in which    -   L¹⁵¹, L¹⁵², L¹⁵³ and L¹⁵⁴ are independently of each other H or        F.

Preferred classes of compounds comprised by formula XV are compounds offormula XV-A to XV-E in which Z¹⁵¹ is a single bond:

in which R¹⁵¹ is defined as above and preferably means a straight-chainalkyl with 1 to 8 carbon atoms, especially a straight-chain alkanyl oralkenyl having 2, 3, 4, 5 or 6 carbon atoms; Z¹⁵² is a C≡C triple bondor preferably a single bond; and L¹⁵¹, L¹⁵², L¹⁵³ and L¹⁵⁴ are H or Fwith L¹⁵¹ and L¹⁵² being preferably H. Preferred compounds of formulasXV-A to XV-E are

in which R¹⁵¹ is as defined above.

Some specific examples of compounds of formula XV are

If these compounds are present in component (α) their total amount mayrange from about 5 to about 45 weight %. It is preferred that only onetype of compounds of formulas XV-A to XV-E are present in the liquidcrystal composition for use in the invention for the same time.

In a further preferred embodiment of the invention the liquid crystalcomposition for use in a bistable liquid crystal device and especiallyin a zenithal bistable nematic liquid crystal device may also comprisesa component (β). Said component (β) may be present in the liquid crystalcomposition in an amount of at least 5 weight % or more. Component (β)may positively influence the clearing point of the liquid crystalcompositions used in bistable liquid crystal devices, i.e. the clearingpoint may be increased by adding component (β). Component (β) comprisescompounds of formula V and/or formula VI and/or formula VII and/orformula VIII and/or formula IX

in which

-   -   g is 0 or 1;    -   R⁵¹, R⁵², R⁶¹, R⁶², R⁷¹, R⁷², R⁸¹, R⁸², R⁹¹ and R⁹² are        independently of each other C₁-C₁₅ alkyl which is unsubstituted        or mono- or poly-substituted with CN or halogen and in which one        or more of the CH₂ groups may be replaced independently of each        other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that        there are no hetero atoms adjacent to each other;    -   L⁵¹ is H or F;    -   Z⁶¹ is —CO—O—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —CH₂CH₂—,        —CF₂CF₂—, —CH₂CF₂—, —CF₂CH₂—, —CH═CH— or —C≡C—;

are independently of each other

in which

-   -   L⁵² and L⁵³ are independently of each other H or F.

Preferred compounds of formula V are of the following formulas:

with R⁵¹ and R⁵² being as defined above. Preferably, in formulas V andV-A to V-G R⁵¹ and R⁵² are both independently of each otherstraight-chain alkyl, more preferred straight-chain alkanyl or alkenylhaving 2, 3, 4, 5 or 6 carbon atoms, especially straight-chain alkanylwith 2 to 6 carbon atoms, a is 1 and L⁵¹ is H or F (for formula V).Highly preferred compounds are of formula V-D and V-E. Especiallypreferred examples of formula V are compounds of formula V1 to V6:

Most preferred compounds of formula V are compounds V2, V4 and V6, andit is preferred to have a mixture of all three compounds in the liquidcrystal composition.

With respect to formula VI preferred compounds are of formulas VI-A andVI-B in which g is 1 as well as of formulas VI-C and VI-D in which g iszero:

with R⁶¹, R⁶² and Z⁶¹ being as defined above; Z⁶¹ is preferably —CO—O—or, in case of formula VI-D, —OCH₂—. R⁶¹ and R⁶² are preferably bothindependently of each other straight-chain alkyl, more preferredstraight-chain alkanyl or alkenyl having 2, 3, 4, 5 or 6 carbon atoms,especially straight-chain alkanyl with 2 to 6 carbon atoms. Compounds offormula VI-B are more preferred. Especially preferred examples offormula VI are compounds of formulas VI1 to VI3 as well as of formulasVI4 and VI5 and of formulas VI6 to VI8:

It is especially preferred to have a mixture of compounds VI1, VI2 andVI3 in the liquid crystal composition.

Preferably, in formula VII R⁷¹ is straight-chain alkyl, especiallystraight-chain alkanyl having 2, 3, 4, 5 or 6 carbon atoms, and R⁷² isstraight-chain alkyl or, more preferred, alkoxy having 1, 2, 3 or 4carbon atoms. Especially preferred examples of formula VII are compoundsof formula VII1 to VII6:

in which n is an integer from 1 to 6, preferably 2, 3 or 4, especially3. Preferred compounds of formula VII are compounds of formula VII2,VII4 and VII6 with n=3 (giving an n-propyl substituent). It is preferredto have a mixture of all three compounds VII2, VII4 and VII6 in theliquid crystal composition.

Preferably, in formula VIII R⁸¹ is straight-chain alkenyl, especiallystraight-chain alkenyl having 2, 3, 4 or 5 carbon atoms, and R⁸² isstraight-chain alkanyl or alkoxy both having 1, 2, 3, 4 or 5 carbonatoms (formula VIII-A or VIII-B with n=2, 3, 4, 5 and m=1, 2, 3, 4, 5).

Preferred compounds of formula VIII are compounds of formula VIII1 toVIII4:

Especially preferred are compounds of formula VIII1, VIII3 and VIII4.They may be used alone or, more preferred, as a mixture of two or threecompounds.

Regarding compounds of formula IX specific compounds are of thefollowing formulas

with R⁹¹ and R⁹² being as defined above. Preferably, R⁹¹ and R⁹² arestraight-chain alkyl, especially alkanyl, with 1, 2, 3, 4, 5 or 6 carbonatoms.

Preferred compounds of formula IX are:

with n and m being independently of each other 1, 2, 3. 4, 5 or 6.Especially preferred examples of compounds of formula IX are

Component (β) may be used in an amount of 5 weight % or more in theliquid crystal composition for use in bistable liquid crystal devicesaccording to the invention. When component (α) comprises at least onecompound of formula III, it is preferred that the liquid crystalcomposition comprises 8 weight % or more of component (β). When there isno compound of formula II in component (α), an amount of at least 10weight % of component (β) is even more preferred. In certain embodimentsof the invention a total amount of 15 or 20 or more weight % ofcomponent (β) is highly preferred.

In an actual embodiment of the invention component (β) may contain oneor more compounds of only one of the formulas V or VI or VII or VIII orIX. It is also possible that it contains one or more compounds of two,three or more of the formulas V to IX. It may contain an equal or adifferent amount of compounds of each formula used. It is preferred thatcomponent (β) contains one or more compounds of one or two of theformulas V, VI, VII, VIII or IX. If compounds of two of the formulas Vto IX are contained, any combination is possible. Both types ofcompounds may be used in an equal amount, or one of the types may beused in an excess with regard to the other one, for instance, in a ratioof 2:1. It is preferred that an equal amount of both types of compoundsis used. When component (α) comprises no compound of formula II, it ispreferred that component (β) comprises compounds of two of the formulasV, VI, VII, VIII or IX.

In another preferred embodiment of the invention the liquid crystalcomposition for use in the bistable liquid crystal device and especiallyin the zenithal bistable nematic device according to the inventionfurther comprises 3 weight % or more of a component (γ) containing oneor more compounds having an optical anisotropy Δn of at least 0.20. Ithas been found that the use of this component (γ) may decrease theoperating voltage V_(opt) of the liquid crystal composition. In general,component (γ) can comprise any (mesogenic) compound exhibiting a Δn ofat least 0.20 that is not detrimental to the set of parameters importantfor use in especially zenithal bistable nematic liquid crystal devices.It is preferred that component (γ) comprises tolanes having a Δn of atleast 0.20, especially at least one tolane compound of formula X:

in which

-   k is 0, 1 or 2;-   R¹⁰¹ and R¹⁰² are independently of each other C₁-C₁₅ alkyl which is    unsubstituted or mono- or poly-substituted with CN or halogen and in    which one or more of the CH₂ groups may be replaced by —O—, —S—,    —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms    adjacent to each other; and

Especially preferred are compounds of formula X-A

in which n and m are independently of each other 1, 2, 3, 4, 5 or 6 andk is 0, 1 or preferably 2. Preferred examples are of formula X-A1 with nbeing 2, 3 or 4 and m being 1, 2, 3, 4 or5:

Among these compounds X-A1a and X-A1b are most preferred:

It should be noted that certain compounds of formula X as well ascompounds having a structure similar to that of formula X in that R¹⁰²is replaced by a fluorine atom may also have a ratio of γ₁/T_(NI) ^(K)of 0.51 mPa·s/K or less, a clearing point T_(NI) of at least 100° C. anda rotational viscosity γ₁ of not more than 190 mPa·s. Those may becomprised by component (δ). Among these compounds are, for instance, thecompound of formula X-A1b (γ₁/T_(NI) ^(K)=0.16; T_(NI)=219° C.; andγ₁=81 mPa·s); and the compound having a structure similar to structureX-A1b in which the butyl substituent on the right-hand ring has beenreplaced by F (γ₁/T_(NI) ^(K)=0.19; T_(NI)=189° C.; and γ₁=89 mPa·s).

If present component (γ) is contained in an amount of at least 3 weight% and more preferred at least 5 weight %. Even much higher amounts of,e.g., up to 50 weight % of component (γ) may be used in specificembodiments of the invention in order to achieve, for instance, veryfast switching.

The liquid crystal composition for use in the bistable liquid crystaldevices and especially in the zenithal bistable nematic liquid crystaldevices of the invention may comprise further substances for adjustingseveral properties of said composition if desired. For example, some ofthese substances may be used for adjusting the viscosity of the liquidcrystal composition. (Hence, if one of these compounds has a ratio ofγ₁/T_(NI) ^(K) of 0.51 mPa·s/K or less, a clearing point T_(NI) of atleast 100° C. and a rotational viscosity γ₁ of not more than 190 mPa·s ,it may be a compound being comprised by component (δ).) In certainembodiments the liquid crystal composition for use in the zenithalbistable nematic devices according to the invention comprises at leastone compound of formula XI and/or at least one compound of formula XIIand/or at least one compound of formula XIII and/or at least onecompound of formula XIV

in which

-   -   R¹¹¹ and R¹⁴² are independently of each other C₂-C₁₅ alkenyl        which is unsubstituted or mono- or poly-substituted with CN or        halogen and in which one or more of the CH₂ groups may be        replaced independently of each other by —O—, —S—, —CH═CH—,        —C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms        adjacent to each other;    -   R¹²¹, R¹³¹, R¹³² and R¹⁴¹ are independently of each other C₁-C₁₅        alkyl which is unsubstituted or mono- or poly-substituted with        CN or halogen and in which one or more of the CH₂ groups may be        replaced independently of each other by —O—, —S—, —CH═CH—,        —C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms        adjacent to each other;    -   R¹²² is C₁-C₁₅ alkyl which is unsubstituted or mono- or        poly-substituted with halogen and in which one or more of the        CH₂ groups may be replaced independently of each other by —O—,        —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no        hetero atoms adjacent to each other;    -   Y¹¹¹ is F or Cl;    -   L¹¹¹ and L¹¹² are independently of each other H or F; and

are independently of each other

The exact nature and amount of these compounds within the liquid crystalcomposition depend on the specific mixture and the desired effect andcan be easily chosen by the skilled person.

Preferred compounds of formula XI are compounds of formula XI-A or XI-B

with n being 2, 3, 4, 5 or 6 and Y¹¹¹ being F or Cl. Especiallypreferred compounds of formula XI are the following compounds:

The most preferred compound of formula XI is compound XI1.

Preferred compounds of formula XII are compounds of formula XIIA, XIIB,XIIC, XIID, XIIE and XIIF:

with n being 1, 2, 3, 4, 5 or 6 and m being 1, 2, 3, 4, 5 or 6. Specificexamples of compounds of formula XII are the following compounds:

Preferred compounds of formula XIII are compounds of formula XIIIA orXIIIB:

with n being 1, 2, 3, 4, 5, 6, 7 or 8 and m being 1, 2, 3, 4, 5 or 6.Especially preferred examples of compounds of formula XIII are thefollowing compounds:

Preferred compounds of formula XIV are compounds of formula XIVA

with n being 1, 2, 3, 4, 5, 6i 7 or 8 and m being 2, 3, 4, 5 or 6Specific examples of compounds of formula XIV are the followingcompounds:

The most preferred compound of formula XIV is compound XIV2.

The liquid crystal composition for the use according to the invention inthe bistable liquid crystal devices may also comprises mesogenicsubstances having a medium dielectric anisotropy of Δε of about 8 to 10or more, for instance one or more compounds of formula XVI and/or one ormore compounds of formula XVII, preferably in an amount of up to 30weight %, more preferred of up to 20 weight %:

in which

-   R¹⁶¹ and R¹⁷¹ are independently of each other C₁-C₁₅ alkyl which is    unsubstituted or mono- or poly-substituted with CN or halogen and in    which one or more of the CH₂ groups may be replaced independently of    each other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that    there are no hetero atoms adjacent to each other;-   Y¹⁶¹ and Y¹⁷¹ are independently of each other F, Cl, C₁-C₁₅ alkanyl    or C₂-C₁₅ alkenyl that are mono- or poly-substituted with halogen,    or C₁-C₁₅ alkoxy, which is mono- or poly-substituted with halogen;-   L¹⁶¹ and L¹⁷¹ are independently of each other H or F; and-   Z¹⁶¹ is —CO—O—, CH₂O or CF₂O.

Preferably these compounds are of formulas XVI-A, XVI-B and XVII-A,respectively:

with n being in all three formulas 1, 2, 3, 4, 5, 6 or 7. Thesesubstances may influence both the operating voltage and the operatingwindow of the liquid crystal composition for use in the zenithalbistable nematic devices of the invention as desired.

The liquid crystal composition for the use according to the invention inthe zenithal bistable nematic liquid crystal devices may also comprisesone or more of the mesogenic substances according to the followingformulas XVIII to XXII. The exact nature and amount of these compoundswithin the liquid crystal composition depend on the specific mixture andthe desired effect and can be easily chosen by the skilled person.

wherein

-   R¹⁸¹, R¹⁸², R²⁰¹, R²¹¹ and R²²¹ are independently of each other    C₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substituted    with CN or halogen and in which one or more of the CH₂ groups may be    replaced independently of each other by —O—, —S—, —CH═CH—, —C≡C—,    —CO—O—, —OC—O— such that there are no hetero atoms adjacent to each    other;-   R¹⁹¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- or    poly-substituted with CN or halogen and in which one or more of the    CH₂ groups may be replaced independently of each other by —O—, —S—,    —C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms adjacent    to each other (i.e. R¹⁹¹ does not represent an alkenyl radical);-   L¹⁹¹, L¹⁹², L²⁰¹, L²⁰², L²⁰³, L²⁰⁴, L²¹¹, L²¹², L²¹³, L²¹⁴, L²¹⁵,    L²¹⁶, L²²¹, L²²², L²²³ and L²²⁴ are independently of each other H or    F; and-   Y¹⁹¹, Y²⁰¹, Y²¹¹ and Y²²¹ are independently of each other F, Cl,    C₁-C₁₅ alkanyl or C₂-C₁₅ alkenyl that are independently of each    other mono- or poly-substituted with halogen, or C₁-C₁₅ alkoxy which    is mono- or poly-substituted with halogen.

Preferred compounds of formula XVIII are of the formula XVIIIA

with n being 1, 2, 3, 4, 5, 6 or 7 and p being 2, 3, 4, 5, 6 or 7. Morepreferred are compounds of formula XVIIIA with n being 1, 2, 3, 4 or 5and p being 2, 3, 4 and 5; especially preferred C_(n)H_(2n+1) is methyl,ethyl or n-propyl and C_(p)H_(2p−1) is a —CH₂—CH₂—CH═CH₂ or—CH₂—CH₂—CH═CH—CH₃ radical the latter preferably with E-configuration ofthe C═C double bond.

Preferred compounds of formula XIX are of the formulas XIXA and XIXB:

with n being 1, 2, 3, 4, 5, 6 or 7 and Y¹⁹¹ being F, Cl, CF₃ or OCF₃.More preferred are compounds of formula XIXB with n being 2, 3, 4, 5, 6or 7 and Y¹⁹¹ being F.

Preferred compounds of formula XX are of the formulas XXA to XXG:

with n being 1, 2, 3, 4, 5, 6 or 7 and Y²⁰¹ being F, Cl, CF₃ or OCF₃.More preferred are compounds of formulas XXB, XXC and XXD with n being2, 3, 4, 5, 6 or 7 and Y²⁰¹ being F.

Preferred compounds of formula XXI are of the formulas XXIA to XXIJ:

with n being 1, 2, 3, 4, 5, 6 or 7 and Y²¹¹ being F, Cl, CF₃ or OCF₃.More preferred are compounds of formula XXID with n being 2, 3, 4, 5, 6or 7 and Y²¹¹ being F.

Preferred compounds of formula XXII are of the formulas XXIA or XXIIB:

with n being 1, 2, 3, 4, 5, 6 or 7 and Y²¹¹ being F, Cl, CF₃ or OCF₃.More preferred are compounds of formula XXIIB with n being 2, 3, 4, 5, 6or 7 and Y²²¹ being F.

It is further preferred that the liquid crystal composition for the useof the invention is a nematic liquid crystal composition.

It will be acknowledged by those skilled in the art that the liquidcrystal composition for the use according to the invention may alsocomprise further (mesogenic) compounds besides those disclosed in moredetail in this specification. A wide variety of mesogenic compounds maybe used as long as they are not detrimental to the set of parametersimportant for the use of the bistable liquid crystal compositionaccording to the invention.

A further subject matter of this invention is a liquid crystal mediumcomprising

-   -   at least at least 30 weight % (based on the total weight of the        composition) of a component (α) containing one or more compounds        having a dielectric anisotropy Δε of at least 25, whereby at        least 25 weight % (based on the total weight of the composition)        of said compounds have a dielectric anisotropy Δε of at least        40; and    -   a component (δ) containing one or more compounds each having a        ratio of γ₁/T_(NI) ^(K) of 0.51 mPa·s/K or less, a clearing        point T_(NI) of at least 100° C. and a rotational viscosity γ₁        of not more than 190 mPa·s (wherein γ₁ is the rotational        viscosity at 20° C. in mPa·s and T_(NI) ^(K) is the clearing        point in degrees Kelvin).

A still further subject matter of the present invention is a liquidcrystal medium comprising

-   -   at least one compound of formula I; and    -   at least one compound of formula II.

Said medium optionally comprises at least one compound of formula IV asdefined above.

Still a further subject matter of the present invention is a liquidcrystal medium comprising

-   -   at least one compound of formula I; and    -   at least one compound of formula III.

Said medium optionally comprises at least one compound of formula IV asdefined above.

The liquid crystal composition for use in the zenithal bistable nematicdevices of the invention may also contain an optically active component(ζ) as a dopant in an amount of 0 to 3 weight %. The chiral dopant maybe useful to remove reverse twist domains in the TN mode. There exists awide variety of compounds suitable as members of component (ζ) all ofwhich are readily available. Exemplary substances arecholesterylnonanoate (CN), S-811, S-1011 and S-2011 and CB15 (MerckKGaA, Darmstadt, Germany). Although S-811 might be a preferred dopant,the specific choice of the dopants is not a critical issue.

The liquid crystal composition for use in the zenithal bistable nematicdevices of the invention may also contain one or more light stabilizersand/or additives like pleochromatic dyes known in the state of the art.

All the compounds used in the liquid crystal composition of the bistableliquid crystal devices are either commercially available or can bereadily prepared by methods known to those skilled in the art and asdescribed in the standard text books of organic synthesis, for instance,in Houben-Weyl, Methoden der Organischen Chemie, Georg-Thieme-Verlag,Stuttgart. The liquid crystal composition will be prepared by applyingstandard protocols and techniques. In general, the desired amount of theminor component(s) will be dissolved in the major component, usuallyunder elevated temperature. Alternatively, solutions of components inorganic solvents like acetone, chloroform or methanol, can be mixed andafterwards the solvent(s) can be removed, e.g., by distillation.Likewise, manufacturing of the bistable devices according to theinvention will follow standard techniques known to the artisan.

In the present description and the following examples the structures ofthe mesogenic compounds disclosed are described by using acronyms. Saidacronyms can be transformed into chemical formulas according to Tables Aand B. In these tables, radicals C_(n)H_(2n+1) and C_(m)H_(2m+1) arestraight-chain alkyl radicals having n and m carbon atoms, respectively.Alkenyl radicals have the trans configuration. The codes according toTable B are self-evident. In Table A, only the acronym for the parentstructure is given. In individual cases, the acronym for the parentstructure is followed, usually separated by a hyphen, by a code for thesubstituents R¹, R², L¹ and L² as given below:

Code of R¹, R², L¹, L² R¹ R² L¹ L² n C_(n)H_(2n + 1) CN H H nmC_(n)H_(2n + 1) C_(m)H_(2m + 1) H H nOm C_(n)H_(2n + 1) OC_(m)H_(2m + 1)H H nF C_(n)H_(2n + 1) F H H nN.F C_(n)H_(2n + 1) CN F H nN.F.FC_(n)H_(2n + 1) CN F F

TABLE A

PTP

CPTP

ME

HP

PCH

CCPC

PDX

D

PYP

K6

TABLE B

CBC-nm

CBC-nmF

CP-nm

CP-nmF

CC-n-V

CCG-V-F

CCP-Vn-m

CCP-V-m

PZU-V2-N

PGU-n-F

CDU-n-F

CCGU-n-F

CCOC-n-m

PP-n-mVp

CVCP-nV-(O)m

PTP-n-(O)m

CPTP-n-(O)m

PPTUI-n-m

TABLE C Table C shows dopants optionally present in the liquid crystalcompositions for use in the zenithal bistable nematic devices of theinvention (component (ζ)).

C 15

CB 15

CM 21

R/S-811

CM 44

CM 45

CM 47

R/S-1011

R/S-3011

CN

R/S-2011

R/S-4011

R/S-5011

TABLE D Table D shows stabilizers optionally present in the liquidcrystal compositions for use in the zenithal bistable nematic devices ofthe invention.

Percentages given herein are weight % and generally related to the totalamount of a composition or mixture except stated otherwise. Temperaturesare given in degree Celsius (° C.) unless stated otherwise. T_(NI) meansthe clearing point at which a nematic medium becomes isotropic. Δn isthe optical anisotropy (birefringence) (at 589 nm, 20° C.). Δε means thedielectric anisotropy (at 1 kHz, 20° C.). K₁ is the splay elasticconstant, and K₃ is the bend elastic constant both given in pN.Electrooptical data has been determined in a VAN zenithal bistablenematic cell. Except stated otherwise the measurements have beenperformed at 20° C. V_(opt) is the corrected operating voltage (in V)derived from the corrected switching field E_(LC@100 μs) (at 25° C.; inzenithal bistable test cells with the actual cell gap d of about 2.8 toabout 5 μm; 100 μs pulse) by V_(opt)=E_(LC@100 μs)·d_(opt) (with d_(opt)(in μm) being λ√3/(2Δn); λ=555 nm). ΔV_(opt) is the corrected operatingwindow at a 400 μs pulse for B-W-switching and reverse switching (in V);it is calculated from the experimental switching field windowΔE_(LC@400 μs) (at 25° C.; 400 μs pulse) multiplied with d_(opt) definedas given above. Optical response time τ_(opt) (in ms) is calculated fromτ_(opt)=τ·d² _(opt)/d² with τ being the experimental response time,d_(opt) being as defined above and d being the experimental cell gap.

The following Examples should further illustrate the present inventionas described above and in the claims but not meant to restrict itsscope.

EXAMPLES

Test samples were prepared by weighing out the appropriate weightamounts (percentage weight/weight) of the individual components. Thesample was then homogenised by heating into the isotropic phase andthoroughly mixing. The mixture was then stirred with a givenconcentration of alumina and then filtered (0.2 μm) to just leave theliquid crystal mixture. The nematic to isotropic transition temperature(or clearing point, T_(NI)), dielectric anisotropy (Δε), birefringence(Δn), splay and bend elastic constants (K₁ and K₃), and rotationalviscosities (γ₁) were determined as described in the Merck brochure“Physical Properties of Liquid Crystals—Description of the measurementmethods”, ed. W. Becker (1998). Values for single compounds areextrapolated from those determined using a known concentration (usually10 weight % of the single compound) in a standard host mixture for whichthe initial mixture values are also known. The electroopticalperformance of each mixture in a zentihal bistable nematic device wasmeasured using a simple experimental set-up and the VAN type test cells.This required a transmissive mode microscope with a mountedphoto-detector connected to an oscilloscope. This allowed thetransmission through crossed polarisers to be monitored. The test cellwas mounted on a heating stage under the microscope to permitmeasurements at 25° C. Bipolar electrical pulses (of varying durationand voltage) were used to ensure that there was no net d.c. voltageapplied to the cell. The trailing edge (and so polarity) of each pulsetherefore determined the final switched state (depending on the durationand voltage). Two signal generators were necessary to ensure that thecorrect initial state is first selected, with the first signaltriggering the second (with an appropriate phase difference). Bothsignals were amplified by passing the output of the signal generatorsthrough an amplifier before being connected to the test cell. For theB-W transition, the voltages required for 10 and 90% transmissionchanges and reverse 90 and 10% transmission changes were measured forvarious pulse durations. For the W-B transition, the voltages requiredfor 90 and 10% transmission changes only were measured for various pulsedurations. These levels were set on the oscilloscope once the 0 and 100%transmission levels were known (i.e. black and white), and they couldalso be used to determine the optical response time of the transition(for 10 to 90% transmission changes).

VAN type test cells were used with cell gaps typically 3-5 μm, intransmissive mode and with crossed polarisers. Due to the varying cellthicknesses and different mixture Δn values, the retardation was notoptimised but this is not crucial as it only decreases the contrast.

Example 1

Compound Amount (wt %) T_(NI) (° C.) 95.0 ME2N.F 10 Δε 46.5 ME3N.F 10 Δn0.1682 ME4N.F 10 K₁ (pN) 9.2 ME5N.F 10 K₃ (pN) 19.1 PZU-V2-N 10 V_(opt)(V) 13.8 CPTP-301 5 ΔV_(opt) (V) 3.9 CPTP-302 5 τ_(opt) (ms) 28 CPTP-3035 CCG-V-F 10 CCP-V-1 10 CCP-V2-1 5 CVCP-V-O1 5 CVCP-1V-O1 5 Total 100

Example 2

Compound Amount (wt %) T_(NI) (° C.) 91.9 ME2N.F 12 Δε 45.3 ME3N.F 12 Δn0.1714 ME4N.F 12 K₁ (pN) 9.2 ME5N.F 12 K₃ (pN) 19.0 HP-3N.F 5 V_(opt)(V) 19.7 HP-4N.F 5 ΔV_(opt) (V) 9.0 HP-5N.F 5 τ_(opt) (ms) 25 CC-5-V 12CCP-V-1 10 CPTP-301 5 CPTP-302 5 CPTP-303 5 Total 100

Example 3

Compound Amount (wt %) T_(NI) (° C.) 95.8 ME2N.F 10 Δε 48.0 ME3N.F 10 Δn0.1816 ME4N.F 10 K₁ (pN) 10.9 ME5N.F 10 K₃ (pN) 18.8 PZU-V2-N 10 V_(opt)(V) 16.0 CPTP-301 5 ΔV_(opt) (V) 8.6 CPTP-302 5 τ_(opt) (ms) 8 CPTP-3035 γ1 (mPa · s) 341 CCP-V-1 15 CCP-V2-1 15 PPTUI-3-2 5 Total 100

Example 4

Compound Amount (wt %) T_(NI) (° C.) 90.9 ME2N.F 9 Δε 45.2 ME3N.F 9 Δn0.2471 ME4N.F 9 K₁ (pN) 11.6 ME5N.F 9 K₃ (pN) 14.6 PZU-V2-N 9 V_(opt)(V) 26.4 PPTUI-3-2 20 τ_(opt) (ms) 1 PPTUI-3-4 25 γ1 (mPa · s) 361CCP-V-1 5 CCP-V2-1 5 Total 100

Example 5

Compound Amount (wt %) T_(NI) (° C.) 97.1 ME2N.F 10 Δε 47.8 ME3N.F 10 Δn0.1569 ME4N.F 10 K₁ (pN) 11.3 ME5N.F 10 K₃ (pN) 19.4 PZU-V2-N 10 V_(opt)(V) 8.7 CCPC-33 5 τ_(opt) (ms) 11 CCPC-34 5 γ1 (mPa · s) 407 CCPC-35 5CCP-V-1 15 CCP-V2-1 15 PPTUI-3-2 5 Total 100

Example 6

Compound Amount (wt %) T_(NI) (° C.) 96.7 ME2N.F 12 Δε 48.3 ME3N.F 12 Δn0.1674 ME4N.F 12 K₁ (pN) 10.0 ME5N.F 12 K₃ (pN) 20.7 HP-3N.F 5 V_(opt)(V) 12.8 HP-4N.F 5 ΔV_(opt) (V) 28.6 HP-5N.F 5 τ_(opt) (ms) 17 CCP-V-116 γ1 (mPa · s) 433 CCP-V2-1 16 PPTUI-3-2 5 Total 100

Example 7

Compound Amount (wt %) T_(NI) (° C.) 90.0 ME2N.F 10 Δε 57.3 ME3N.F 10 Δn0.1816 ME4N.F 10 K₁ (pN) 8.4 ME5N.F 10 K₃ (pN) 16.1 PZU-V2-N 10 V_(opt)(V) 11.7 HP-3N.F 5 ΔV_(opt) (V) 8.5 HP-4N.F 5 τ_(opt) (ms) 18 HP-5N.F 5CC-5-V 9 CCP-V-1 4 CCP-V2-1 4 CPTP-301 5 CPTP-302 5 CPTP-303 5 PPTUI-3-23 Total 100

Example 8

Compound Amount (wt %) T_(NI) (° C.) 93.5 ME2N.F 10 Δε 48.4 ME3N.F 10 Δn0.1528 ME4N.F 10 K₁ (pN) 10.5 ME5N.F 10 K₃ (pN) 20.1 PZU-V2-N 10 V_(opt)(V) 8.7 CC-5-V 6 ΔV_(opt) (V) 7.3 CCP-V-1 10 τ_(opt) (ms) 20 CCP-V2-1 10CBC-33F 4 CBC-53F 4 CBC-55F 4 CBC-33 4 CBC-53 4 CBC-55 4 Total 100

Example 9

Compound Amount (wt %) T_(NI) (° C.) 93.4 ME2N.F 10 Δε 72.0 ME3N.F 10 Δn0.1842 ME4N.F 10 K₁ (pN) 7.1 ME5N.F 10 K₃ (pN) 16.7 PZU-V2-N 15 V_(opt)(V) 10.6 HP-3N.F 5 ΔV_(opt) (V) 8.5 HP-4N.F 5 τ_(opt) (ms) 27 HP-5N.F 5CCP-V-1 8 CCP-V2-1 7 CPTP-301 5 CPTP-302 5 CPTP-303 5 Total 100

Example 10

Compound Amount (wt %) T_(NI) (° C.) 90.7 ME2N.F 10 Δε 45.9 ME3N.F 10 Δn0.1569 ME4N.F 10 K₁ (pN) 9.9 ME5N.F 10 K₃ (pN) 18.1 PZU-V2-N 10 V_(opt)(V) 11.4 CCP-V-1 15 ΔV_(opt) (V) 11.2 CCP-V2-1 15 τ_(opt) (ms) 17PPTUI-3-2 5 γ1 (mPa · s) 290 CVCP-V-1 5 CVCP-V-O1 5 CVCP-1V-O1 5 Total100

Example 11

Compound Amount (wt %) T_(NI) (° C.) 95.9 ME2N.F 10 Δε 51.2 ME3N.F 10 Δn0.1639 ME4N.F 10 K₁ (pN) 10.8 ME5N.F 10 K₃ (pN) 18.2 PZU-V2-N 10 V_(opt)(V) 10.7 CCP-V-1 15 τ_(opt) (ms) 17 CCP-V2-1 15 PPTUI-3-2 5 CBC-33F 5CBC-53F 5 CBC-55F 5 Total 100

Example 12

Compound Amount (wt %) T_(NI) (° C.) 91.3 ME2N.F 10 Δε 55.8 ME3N.F 10 Δn0.1801 ME4N.F 10 K₁ (pN) 9.7 ME5N.F 10 K₃ (pN) 15.3 PZU-V2-N 14 V_(opt)(V) 17.4 CCP-V-1 8 ΔV_(opt) (V) 9.5 CCP-V2-1 8 τ_(opt) (ms) 33 PPTUI-3-25 CPTP-301 5 CPTP-302 5 CPTP-303 5 CC-5-V 4 CCPC-33 2 CCPC-34 2 CCPC-352 Total 100

Example 13

Compound Amount (wt %) T_(NI) (° C.) 96.2 ME2N.F 12 Δε 47.3 ME3N.F 12 Δn0.1737 ME4N.F 12 K₁ (pN) 9.8 ME5N.F 12 K₃ (pN) 20.4 HP-3N.F 5 V_(opt)(V) 17.0 HP-4N.F 5 τ_(opt) (ms) 18 HP-5N.F 5 CCP-V-1 10 CCP-V2-1 10CBC-33F 3 CBC-53F 3 CBC-55F 3 PTP-201 4 PTP-301 4 Total 100

Example 14

Compound Amount (wt %) T_(NI) (° C.) 95.3 PZU-V2-N 10 Δε 49.2 ME2N.F 10Δn 0.1420 ME3N.F 10 K₁ (pN) 9.7 ME4N.F 10 K₃ (pN) 17.1 ME5N.F 10 V_(opt)(V) 8.6 CCPC-33 4 τ_(opt) (ms) 30 CCPC-34 4 CCPC-35 4 CCP-V-1 8 CCP-V2-18 CC-5-V 10 CBC-33F 4 CBC-35F 4 CBC-55F 4 Total 100

Example 15

Compound Amount (wt %) T_(NI) (° C.) 97.3 ME2N.F 10 Δε 34.3 ME3N.F 10 Δn0.1393 ME4N.F 10 K₁ (pN) 10.8 ME5N.F 10 K₃ (pN) 17.9 ME7N.F 10 V_(opt)(V) 14.4 CCPC-33 4 τ_(opt) (ms) 24 CCPC-34 4 CCPC-35 4 CCP-V-1 6CCP-V2-1 6 CC-5-V 14 CBC-33F 4 CBC-35F 4 CBC-55F 4 Total 100

Example 16

Compound Amount (wt %) T_(NI) (° C.) 85.6 PZU-V2-N 20 Δε 44.2 ME3N.F.F10 Δn 0.1106 CDU-2-F 10 K₁ (pN) 9.1 CDU-3-F 10 K₃ (pN) 17.9 CDU-5-F 10V_(opt) (V) 5.9 CC-5-V 5 ΔV_(opt) (V) 33.5 CCP-V-1 10 τ_(opt) (ms) 34CCP-V2-1 10 CCPC-33 5 CCPC-34 5 CCPC-35 5 Total 100

Example 17

Compound Amount (wt %) T_(NI) (° C.) 95.5 PZU-V2-N 20 Δε 54.3 ME3N.F.F10 Δn 0.1741 PGU-2-F 10 K₁ (pN) 9.3 PGU-3-F 10 K₃ (pN) 17.0 PGU-5-F 10V_(opt) (V) 5.6 CCP-V-1 15 ΔV_(opt) (V) 21.1 CCP-V2-1 10 τ_(opt) (ms) 17CCPC-33 5 CCPC-34 5 CCPC-35 5 Total 100

Example 18

Compound Amount (wt %) T_(NI) (° C.) 92.2 PZU-V2-N 20 Δε 47.2 ME2N.F 7Δn 0.1341 ME3N.F 6 K₁ (pN) 10.3 ME4N.F 4 K₃ (pN) 18.3 ME5N.F 3 V_(opt)(V) 7.8 CDU-2-F 5 τ_(opt) (ms) 21 CDU-3-F 5 CDU-5-F 5 PP-1-2V1 6 CCP-V-112 CCP-V2-1 12 CCPC-33 5 CCPC-34 5 CCPC-35 5 Total 100

Example 19

Compound Amount (wt %) T_(NI) (° C.) 106.2 PZU-V2-N 19 Δε 57.4 ME2N.F 5Δn 0.1534 ME3N.F 5 K₁ (pN) 7.8 ME4N.F 5 K₃ (pN) 12.7 ME5N.F 5 V_(opt)(V) 6.5 PGU-2-F 5 ΔV_(opt) (V) 31.1 PGU-3-F 5 τ_(opt) (ms) 29 PGU-5-F 5CCGU-3-F 5 CCP-V-1 13 CCP-V2-1 13 CCPC-33 5 CCPC-34 5 CCPC-35 5 Total100

Example 20

Compound Amount (wt %) T_(NI) (° C.) 91.7 PZU-V2-N 15 Δε 39.0 ME2N.F 5Δn 0.1195 ME3N.F 5 K₁ (pN) 10.3 ME4N.F 5 K₃ (pN) 17.3 ME5N.F 5 V_(opt)(V) 5.4 CDU-2-F 5 ΔV_(opt) (V) 19.6 CDU-3-F 5 τ_(opt) (ms) 30 CDU-5-F 5CCGU-3-F 5 CCP-V-1 15 CCP-V2-1 15 CCOC-3-3 5 CCOC-3-5 5 CCOC-4-3 5 Total100

Example 21

Compound Amount (wt %) T_(NI) (° C.) 102.5 PZU-V2-N 20 Δε 47.8 ME2N.F 5Δn 0.1462 ME3N.F 5 K₁ (pN) 12.1 ME4N.F 5 K₃ (pN) 20.2 ME5N.F 5 V_(opt)(V) 5.9 CCGU-3-F 5 ΔV_(opt) (V) 30.6 PP-1-2V1 10 τ_(opt) (ms) 16 CCP-V-115 CCP-V2-1 15 CCPC-33 5 CCPC-34 5 CCPC-35 5 Total 100

Example 22

Compound Amount (wt %) T_(NI) (° C.) 84.7 PZU-V2-N 25 Δε 40.5 PCH-3N.F.F5 Δn 0.1532 PGU-2-F 10 K₁ (pN) 10.0 PGU-3-F 10 K₃ (pN) 16.8 PGU-5-F 10V_(opt) (V) 6.1 CCP-V-1 15 ΔV_(opt) (V) 7.8 CCP-V2-1 10 τ_(opt) (ms) 34CCPC-33 5 CCPC-34 5 CCPC-35 5 Total 100

Comparative Example

MLC-6204 (Merck KGaA, Darmstadt) was tested under similar conditions asthe Examples according to the invention:

T_(NI) (° C.) 62.4 Δε 35.2 Δn 0.1484 K₁ (pN) 7.5 K₃ (pN) 14.8 V_(opt)(V) 11.8 ΔV_(opt) (V) 7.3 τ_(opt) (ms) 41 γ1 (mPa · s) 358

1. A method of generating an electrooptical effect comprising applying avoltage to a liquid crystal device containing a liquid crystalcomposition, said composition comprising: at least 30 weight %, based onthe total weight of the composition, of a component (α) containing oneor more compounds having a dielectric anisotropy Δε of at least 25,wherein at least 25 weight %, based on the total weight of thecomposition, of said compounds have a dielectric anisotropy Δε of atleast 40; and a component (δ) containing one or more compounds eachhaving a ratio of γ₁/T_(NI) ^(K) of 0.51 mPa·s/K or less, a clearingpoint T_(NI) of at least 100° C. and a rotational viscosity γ₁ of notmore than 190 mPa·s, wherein γ₁ is the rotational viscosity at 20° C. inmPa·s and T_(NI) ^(K) is the clearing point in degrees Kelvin.
 2. Amethod according to claim 1, wherein said liquid crystal device is azenithal bistable nematic liquid crystal device.
 3. A method accordingto claim 1, wherein said component (δ) comprises at least one compoundof formula I

in which R¹¹ and R¹² are independently of each other C₁-C₁₅ alkyl whichis unsubstituted or mono- or poly-substituted with CN or halogen and inwhich one or more of the CH₂ groups may be replaced independently ofeach other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that thereare no hetero atoms adjacent to each other;

L¹¹ and L¹² are independently of each other H or F;

L¹³ and L¹⁴ are independently of each other H or F.
 4. A methodaccording to claim 1, wherein said component (α) comprises at least onecompound of formula II and/or at least one compound of formula III

in which a, b, c and d are independently of each other 0, 1, 2, 3 or 4;R²¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substitutedwith CN or halogen and in which one or more of the CH₂ groups may bereplaced independently of each other by —O—, —S—, —CH═CH—, —C≡C—,—CO—O—, —OC—O— such that there are no hetero atoms adjacent to eachother; R³¹ is C₂-C₁₅ alkenyl which is unsubstituted or mono- orpoly-substituted with CN or halogen and in which one or more of the CH₂groups may be replaced independently of each other by —O—, —S—, —CH═CH—,—C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms adjacent toeach other; and Z²¹ and Z³¹ are independently of each other a singlebond or —C≡C—.
 5. A method according to claim 4, wherein said component(α) further comprises at least one compound of formula IV

in which e and f are independently of each other 0, 1, 2, 3 or 4; R⁴¹ isC₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substituted with CNor halogen and in which one or more of the CH₂ groups may be replacedindependently of each other by —O—, —S—, —C≡C—, —CO—O—, —OC—O— such thatthere are no hetero atoms adjacent to each other; and Z⁴¹ is a singlebond or —C≡C—.
 6. A method according to claim 3, wherein R¹¹ is C₂-C₁₅alkenyl which is unsubstituted or mono- or poly-substituted with CN orhalogen and in which one or more of the CH₂ groups may be replacedindependently of each other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O—such that there are no hetero atoms adjacent to each other;


7. A method according to claim 1, wherein said liquid crystalcomposition further comprises at least 5 weight %, based on the totalweight of the composition, of a component (β) comprising at least onecompound selected from the compounds of formula V, VI, VII, VIII and IX

in which g is 0 or 1; R⁵¹, R⁵², R⁶¹, R⁶², R⁷¹, R⁷², R⁸¹, R⁸², R⁹¹ andR⁹² are independently of each other C₁-C₁₅ alkyl which is unsubstitutedor mono- or poly-substituted with CN or halogen and in which one or moreof the CH₂ groups may be replaced independently of each other by —O—,—S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atomsadjacent to each other; L⁵¹ is H or F; Z⁶¹ is —CO—O—, —CH₂O—, —OCH₂—,—CF₂O—, —OCF₂—, —CH₂CH₂—, —CF₂CF₂—, —CH₂CF₂—, —CF₂CH₂—, —CH═CH— or—C≡C—;

are independently of each other

and L⁵² and L⁵³ are independently of each other H or F.
 8. A methodaccording to claim 1, wherein said liquid crystal composition furthercomprises at least 3 weight %, based on the total weight of thecomposition, of a component (γ) containing one or more compounds havingan optical anisotropy Δn of at least 0.20.
 9. A method according toclaim 8, wherein said component (γ) comprises at least one compound offormula X

in which k is 0, 1 or 2; R¹⁰¹ and R¹⁰² are independently of each otherC₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substituted with CNor halogen and in which one or more of the CH₂ groups may be replaced by—O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no heteroatoms adjacent to each other; and


10. A method according to claim 3, wherein said liquid crystalcomposition further comprises at least one compound of formula XI and/orat least one compound of formula XII and/or at least one compound offormula XIII at least one compound of formula XIV

in which R¹¹¹ and R¹⁴² are independently of each other C₂-C₁₅ alkenylwhich is unsubstituted or mono- or poly-substituted with CN or halogenand in which one or more of the CH₂ groups may be replaced independentlyof each other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such thatthere are no hetero atoms adjacent to each other; R¹²¹, R¹³¹, R¹³² andR¹⁴¹ are independently of each other C₁-C₁₅ alkyl which is unsubstitutedor mono- or poly-substituted with CN or halogen and in which one or moreof the CH₂ groups may be replaced independently of each other by —O—,—S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atomsadjacent to each other; R¹²² is C₁-C₁₅ alkyl which is unsubstituted ormono- or poly-substituted with halogen and in which one or more of theCH₂ groups may be replaced independently of each other by —O—, —S—,—CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atomsadjacent to each other; Y¹¹¹ is F or Cl; L¹¹¹ and L¹¹² are independentlyof each other H or F; and

and are independently of each other


11. A method according to claim 1, wherein said liquid crystalcomposition comprises at least 50 weight %, based on the total weight ofthe composition, of said component (α).
 12. A method according to claim1, wherein said liquid crystal composition comprises at least 50 weight%, based on the total weight of the composition, of said component (α)whereby at least 30 weight %, based on the total weight of thecomposition, of said compounds have a dielectric anisotropy Δε of atleast
 40. 13. A method according to claim 1, wherein said liquid crystalcomposition comprises at least 5 weight %, based on the total weight ofthe composition, of said component (δ).
 14. A method according to claim1, wherein said liquid crystal composition comprises at least onecompound of formula XVI and/or XVII and/or of formula XVIII and/or offormula XIX and/or of formula XX and/or of formula XXI and/or of formulaXXII:

in which R¹⁶¹, R¹⁷¹, R¹⁸¹, R¹⁸², R²⁰¹, R²¹¹ and R²²¹ are independentlyof each other C₁-C₁₅ alkyl which is unsubstituted or mono- orpoly-substituted with CN or halogen and in which one or more of the CH₂groups may be replaced independently of each other by —O—, —S—, —CH═CH—,—C═C—, —CO—O—, —OC—O— such that there are no hetero atoms adjacent toeach other; R¹⁹¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- orpoly-substituted with CN or halogen and in which one or more of the CH₂groups may be replaced independently of each other by —O—, —S—, —C≡C—,—CO—O—, —OC—O— such that there are no hetero atoms adjacent to eachother; Y¹⁶¹, Y¹⁷¹, Y¹⁹¹, Y²⁰¹, Y²¹¹ and Y²²¹ are independently of eachother F, Cl, C₁-C₁₅ alkanyl or C₂-C₁₅ alkenyl that are independently ofeach other mono- or poly-substituted with halogen, or C₁-C₁₅ alkoxy,which is mono- or poly-substituted with halogen; L¹⁶¹, L¹⁷¹, L¹⁹¹, L¹⁹²,L²⁰¹, L²⁰², L²⁰³, L²⁰⁴, L²¹¹, L²¹², L²¹³, L²¹⁴, L²¹⁵, L²¹⁶, L²²¹, L²²²,L²²³ and L²²⁴ are independently of each other H or F; and Z¹⁶¹ is—CO—O—, CH₂O or CF₂O.
 15. A liquid crystal medium comprising at least 30weight %, based on the total weight of the composition, of a component(α) containing one or more compounds having a dielectric anisotropy Δεof at least 25, wherein at least 25 weight %, based on the total weightof the composition, of said compounds have a dielectric anisotropy Δε ofat least 40; and a component (δ) containing one or more compounds eachhaving a ratio of γ₁/T_(NI) ^(K) of 0.51 mPa·s/K or less, a clearingpoint T_(NI) of at least 100° C. and a rotational viscosity γ₁ of notmore than 190 mPa·s, wherein γ₁ is the rotational viscosity at 20° C. inmPa·s and T_(NI) ^(K) is the clearing point in degrees Kelvin; whereinsaid component (δ) comprises at least one compound of formula I

in which R¹¹ and R¹² are independently of each other C₁-C₁₅ alkyl whichis unsubstituted or mono- or poly-substituted with CN or halogen and inwhich one or more of the CH₂ group may be replaced independently of eachother —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are nohetero atoms adjacent to each other;

L¹¹ and L¹² are independently of each other H or F;

and L¹³ and L¹⁴ are independently of each other H or F; and saidcomponent (α) comprises at least one compound of formula III

in which c and d are independently of each other 0, 1, 2, 3 or 4; R³¹ isC₂-C₁₅ alkenyl which is unsubstituted or mono- or poly-substituted withCN or halogen and in which one or more of the CH₂ groups may be replacedindependently of each other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O—such that there are no hetero atoms adjacent to each other; and Z³¹ is asingle bond or —C≡C—.
 16. A liquid crystal medium according to claim 15,wherein said component (α) further comprises at least one compound offormula II

in which a and b are independently of each other 0, 1, 2, 3 or 4; R²¹ isC₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substituted with CNor halogen and in which one or more of the CH₂ groups may be replacedindependently of each other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O—such that there are no hetero atoms adjacent to each other; and Z²¹ is asingle bond or —C≡C—.
 17. A liquid crystal medium according to claim 16,wherein said component (α) further comprises at least one compound offormula IV

in which e and f are independently of each other 0, 1, 2, 3 or 4; R⁴¹ isC₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substituted with CNor halogen and in which one or more of the CH₂ groups may be replacedindependently of each other by —O—, —S—, —C≡C—, —CO—O—, —OC—O— such thatthere are no hetero atoms adjacent to each other; and Z⁴¹ is a singlebond or —C≡C—.
 18. A bistable liquid crystal device comprising: twoouter substrates which, together with a frame, form a cell; a liquidcrystal composition present in said cell; and electrode structures withalignment layers on the inside of said outer substrates wherein at leastone alignment layer comprises an alignment grating that permits thecompounds of said liquid crystal composition to adopt at least twodifferent stable states and wherein the assembly of said electrodestructures with said alignment layers being such that a switchingbetween the said at least two different stable states is achieved byapplying suitable electric signals to said electrode structures; whereinsaid liquid crystal composition comprises at least 30 weight %, based onthe total weight of the composition, of a component (α) containing oneor more compounds having a dielectric anisotropy Δε of at least 25,wherein at least 25 weight %, based on the total weight of thecomposition, of said compounds have a dielectric anisotropy Δε of atleast 40; and a component (δ) containing one or more compounds having aratio of γ₁/T_(NI) ^(K) of 0.51 mPa·s/K or less, a clearing point T_(NI)of at least 100° C. and a rotational viscosity γ₁ of not more than 190mPa·s, wherein γ₁ is the rotational viscosity at 20° C. in mPa·s andT_(NI) ^(K) is the clearing point in degrees Kelvin.
 19. A bistableliquid crystal device according to claim 18, wherein said device is azenithal bistable nematic liquid crystal device; and said electrodestructures with alignment layers on the inside of said outer substrateshave at least one alignment layer that comprises an alignment gratingthat permits the compounds of said liquid crystal composition to adoptat least two different stable states with different pretilt angles inthe same azimuthal plane.
 20. A bistable liquid crystal device accordingto claim 18, wherein said component (δ) comprises at least one compoundof formula I

in which R¹¹ and R¹² are independently of each other C₁-C₁₅ alkyl whichis unsubstituted or mono- or poly-substituted with CN or halogen and inwhich one or more of the CH₂ groups may be replaced independently ofeach other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that thereare no hetero atoms adjacent to each other;

in which L¹¹ and L¹² are independently of each other H or F;

and L¹³ and L¹⁴ are independently of each other H or F.
 21. A bistableliquid crystal device according to claim 18, wherein said device is azenithal bistable nematic liquid crystal device, and said component (α)comprises at least one compound of formula II and/or at least onecompound of formula III

in which a, b, c and d are independently of each other 0, 1, 2, 3 or 4;R²¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substitutedwith CN or halogen and in which one or more of the CH₂ groups may bereplaced independently of each other by —O—, —S—, —CH═CH—, —C≡C—,—CO—O—, —OC—O— such that there are no hetero atoms adjacent to eachother; R³¹ is C₂-C₁₅ alkenyl which is unsubstituted or mono- orpoly-substituted with CN or halogen and in which one or more of the CH₂groups may be replaced independently of each other by —O—, —S—, —CH═CH—,—C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms adjacent toeach other; and Z²¹ and Z³¹ are independently of each other a singlebond or —C≡C—.
 22. A bistable liquid crystal device according to claim21, wherein said component (α) further comprises at least one compoundof formula IV

in which e and f are independently of each other 0, 1, 2, 3 or 4; R⁴¹ isC₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substituted with CNor halogen and in which one or more of the CH₂ groups may be replacedindependently of each other by —O—, —S—, —C≡C—, —CO—O—, —OC—O— such thatthere are no hetero atoms adjacent to each other; and Z⁴¹ is a singlebond or —C≡C—.
 23. A bistable liquid crystal device according to claim20, wherein said device is a zenithal bistable nematic liquid crystaldevice, and said liquid crystal composition further comprises at least 5weight %, based on the total weight of the composition, of a component(β) comprising at least one compound selected from the group consistingof compounds of formula V, VI, VII, VIII and IX

in which g is 0 or 1; R⁵¹, R⁵², R⁶¹, R⁶², R⁷¹, R⁷², R⁸¹, R⁸², R⁹¹ andR⁹² are independently of each other C₁-C₁₅ alkyl which is unsubstitutedor mono- or poly-substituted with CN or halogen and in which one or moreof the CH₂ groups may be replaced independently of each other by —O—,—S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atomsadjacent to each other; L⁵¹ is H or F; Z⁶¹ is —CO—O—, —CH₂O—, —OCH₂—,—CF₂O—, —OCF₂—, —CH₂CH₂—, —CF₂CF₂—, —CH₂CF₂—, —CF₂CH₂—, —CH═CH— or—C≡C—;

are independently of each other

and L⁵² and L⁵³ are independently of each other H or F.
 24. A bistableliquid crystal device according to claim 18, wherein said device is azenithal bistable nematic liquid crystal device, and said liquid crystalcomposition further comprises at least 3 weight %, based on the totalweight of the composition, of a component (γ) containing one or morecompounds having an optical anisotropy Δn of at least 0.20.
 25. Abistable liquid crystal device according to claim 24, wherein saidcomponent (γ) comprises at least one compound of formula X

in which k is 0, 1 or 2; R¹⁰¹ and R¹⁰² are independently of each otherC₁-C₁₅ alkyl which is unsubstituted or mono- or poly-substituted with CNor halogen and in which one or more of the CH₂ groups may be replaced by—O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no heteroatoms adjacent to each other; and


26. A bistable liquid crystal device according to claim 20, wherein saiddevice is a zenithal bistable nematic liquid crystal device, and saidliquid crystal composition further comprises at least one compound offormula XI and/or at least one compound of formula XII and/or at leastone compound of formula XIII at least one compound of formula XIV

in which R¹¹¹ and R¹⁴² are independently of each other C₂-C₁₅ alkenylwhich is unsubstituted or mono- or poly-substituted with CN or halogenand in which one or more of the CH₂ groups may be replaced independentlyof each other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such thatthere are no hetero atoms adjacent to each other; R¹²¹, R¹³¹, R¹³² andR¹⁴¹ are independently of each other C₁-C₁₅ alkyl which is unsubstitutedor mono- or poly-substituted with CN or halogen and in which one or moreof the CH₂ groups may be replaced independently of each other by —O—,—S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atomsadjacent to each other; R¹²² is C₁-C₁₅ alkyl which is unsubstituted ormono- or poly-substituted with halogen and in which one or more of theCH₂ groups may be replaced independently of each other by —O—, —S—,—CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are no hetero atomsadjacent to each other; Y¹¹¹ is F or Cl; L¹¹¹ and L¹¹² are independentlyof each other H or F; and

and are independently of each other


27. A liquid crystal device according to claim 18, wherein said liquidcrystal composition comprises at least one compound of formula XVIand/or XVII and/or of formula XVIII and/or of formula XIX and/or offormula XX and/or of formula XXI and/or of formula XXII:

in which R¹⁶¹, R¹⁷¹, R¹⁸¹, R¹⁸², R²⁰¹, R²¹¹ and R²²¹ are independentlyof each other C₁-C₁₅ alkyl which is unsubstituted or mono- orpoly-substituted with CN or halogen and in which one or more of the CH₂groups may be replaced independently of each other by —O—, —S—, —CH═CH—,—C≡C—, —CO—O—, —OC—O— such that there are no hetero atoms adjacent toeach other; R¹⁹¹ is C₁-C₁₅ alkyl which is unsubstituted or mono- orpoly-substituted with CN or halogen and in which one or more of the CH₂groups may be replaced independently of each other by —O—, —S—, —C≡C—,—CO—O—, —OC—O— such that there are no hetero atoms adjacent to eachother; Y¹⁶¹, Y¹⁷¹, Y¹⁹¹, Y²⁰¹, Y²¹¹ and Y²²¹ are independently of eachother F, Cl, C₁-C₁₅ alkanyl or C₂-C₁₅ alkenyl that are independently ofeach other mono- or poly-substituted with halogen, or C₁-C₁₅ alkoxy,which is mono- or poly-substituted with halogen; L¹⁶¹, L¹⁷¹, L¹⁹¹, L¹⁹²,L²⁰¹, L²⁰², L²⁰³, L²⁰⁴, L²¹¹, L²¹², L²¹³, L²¹⁴, L²¹⁵, L²¹⁶, L²²¹, L²²²,L²²³ and L²²⁴ are independently of each other H or F; and Z¹⁶¹ is—CO—O—, CH₂O or CF₂O.
 28. A method according to claim 1, wherein saidcomponent (δ) comprises at least one compound of formula I

in which R¹¹ and R¹² are independently of each other C₁-C₁₅ alkyl whichis ubsubstituted or mono- or poly-substituted with CN or halogen and inwhich one or more of the CH₂ group may be replaced independently or eachother by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that there are nohetero atoms adjacent to each other;

L¹¹ and L¹² are independently of each other H or F; and

and L¹³ and L¹⁴ are independently of each other H or F; and saidcomponent (α) comprises at least one compound of formula III

in which c and d are independently of each other 0, 1, 2, 3, or 4; R³¹is C₂-C₁₅ alkenyl which is unsubstituted or mono- or poly-substitutedwith CN or halogen and in which one or more of the CH₂ groups may bereplaced independently of each other by —O—, —S—, —C≡C—, —CO—O—, —OC—O—such that there are no hetero atoms adjacent to each other; and Z³¹ is asingle bond or —C≡C—.
 29. A liquid crystal device according to claim 18,wherein said component (δ) comprises at least one compound of formula I

in which R¹¹ and R¹² are independently of each other C₁-C₁₅ alkyl whichis unsubstituted or mono- or poly-substituted with CN or halogen and inwhich one or more of the CH₂ groups may be replaced independently ofeach other by —O—, —S—, —CH═CH—, —C≡C—, —CO—O—, —OC—O— such that thereare no hetero atoms adjacent to each other;

L¹¹ and L¹² are independently of each other H or F;

and L¹³ and L¹⁴ are independently of each other H or F; and saidcomponent (α) comprises at least one compound of formula III

in which c and d are independently of each other 0, 1, 2, 3, or 4; R³¹is C₂-C₁₅ alkenyl which is unsubstituted or mono- or poly-substitutedwith CN or halogen and in which one or more of the CH₂ groups may bereplaced independently of each other by —O—, —S—, —C≡C—, —CO—O—, —OC—O—such that there are no hetero atoms adjacent to each other; and Z³¹ is asingle bond or —C≡C—.
 30. A method according to claim 1, wherein saidliquid crystal composition has a clearing point T_(NI) of at least 90°C.
 31. A liquid crystal medium according to claim 15, wherein saidliquid crystal medium has a clearing point T_(NI) of at least 90° C. 32.A liquid crystal device according to claim 18, wherein said liquidcrystal composition has a clearing T_(NI) of at least 90° C.